Elektro Rules Paper

ELEKTRO RULES

Their use and scales

Robert Adams BE

Introduction Of the speciality rules, perhaps the most ubiquitous is the “Elektro” rule, almost every manufacturer of

slide rules produced an Elektro rule. This paper examines the design of such rules and poses a few

questions on the layout of the scales and their overall usefulness.

Definition of an “Elektro” Rule A rule to aid the electrical engineer in solving specific problems. It is usually a rule with the scales of the

standard Rietz system, supplemented with Log Log scales, motor/dynamo efficiency scales and a scale for

voltage drop calculation. The calculations are normally limited to power system frequencies i.e. 0 (Direct

Current) to a few hundred Hertz (Hz). Slide rules designed for Electronic engineering do exist; their main

forte is the calculation of impedance of circuit elements in the higher frequency ranges i.e. 0.1 to 100

MHz. This paper concerns the rules that were primarily used in electrical engineering and not electronic

engineering.

Electrical Engineering Problems they where intended to solve The first “Elektro” slide rules were primarily designed to perform two types of calculations:

• Efficiency of motors and dynamos

• Voltage loss in cables

For motors and generators (dynamos) the efficiency was, in the case of a motor, the ratio of the

mechanical energy output divided by the electrical energy input. In the case of a generator, it was the ratio

of the mechanical energy input divided by the electrical energy output.

The calculation was basically very simple apart from the fact that the units of energy were different, HP

(horsepower) for mechanical energy and KW (kilowatts) for electrical energy.

The calculation of voltage loss in cables was not that much more complicated.

The voltage loss was given by Ohms law:

RIV *= (Volts = current (amps) * resistance (ohms))

The resistance was given by:

ALR

δ*= (Resistance (ohms) = length (m) * resistivity (ohm-metre) / sectional area (m

2))

But as usual in the real world, different countries and cultures use many different measurement units

which invariably add a few complicating factors that require some explanation.

There were at least two different units for horsepower. The Imperial system, used in the British

Commonwealth countries and the US, was based on the required energy to lift a 550 pound weight

through 1 foot in one second and was equivalent to 746 watts. The second, used in mainly in Continental

Europe i.e. users of the metric system, was based on the energy to lift 75 kilograms through 1 metre in 1

second and was equivalent to 736 (or even 735) watts. The latter marks are usually shown as PS on

European rules and are derived from the German word Pferdestärke. The difference in the number of

watts for the PS mark is due to the derivation of the unit using 9.8 or 9.81 m/s2 for the gravitational

constant.

Different units of area were also used. In the metric system, the sectional area of the cable was normally

given in square millimetres. In the Imperial system it could be either square inches or circular mils. This

latter unit was slightly unusual as it was based on the diameter of the conductor, in 1/1000ths of an inch

squared.

Calculations using the base measurement units (i.e. inch, yard, metre) would result in values that were not

usually practical for real world observation and more usual units of 10mm2 and 10 metres or 10yards and

0.01sq. inches were used.

The resistivity/conductivity can be expressed as a value either at 0°C (32° F) or more usually at 20°C (68°

F). Typical values for copper are 1.67 * 10-8

ohm-metres resistivity at 20°C or a conductivity of 5.98 * 10

7

at the same temperature. As electrical conductors could be made of differing purity and alloys of copper it

should be stressed that the specific values for resistivity and conductivity are not unique. Many

manufacturers placed gauge marks for conductor on their rules but usually the calculator needed to be

aware of the specific properties of the cable they where using.

Some rules have gauge points for the use of metals other than copper. For example aluminium, is

particularly important in the modern world where it has nearly taken over from copper as the electricity

distribution industry conductor of choice.

The First Elektro Slide Rule? Here I have relied upon the books by Peter Hopp ref [6] and Dieter von Jezierski ref [5] for information on

catalogues, registered designs and also patents. The earliest mention of a patent for a slide rule for

electrical calculations is the 1890 patent number 1302 awarded to a Mr A.P. Trotter for a slide rule for

electrical calculations with two slides – “Wiring Slide Rule”, it is unknown whether an actual rule based

on this patent was actually produced.

The earliest reference to an actual “Electro” (sic) was in Dieter’s book “Slide Rules. A Journey through

Three Centuries”. In the list of Registered Designs, a design number of 334146 is registered to Nestler in

1908 for the Slide Rule Electro 32.

In his book ref [6] Peter Hopp refers to a “Slide rule for electrical calculations” which was produced by

A.E Colgate of New York in 1901, however the scale layout is unknown. Peter Hopp also mentions two

other American rules which were made by the Lewis Institute of Chicago and called the “Woodworth’s

sliderule for electrical wireman” and the “Woodworth’s sliderule for calculations with volts, amperes,

ohms and watts”. Both rules according to Hopp date from 1909, however again the scale layout of these

rules is unknown. The earliest example in the United States of an actual rule for electrical engineering is

the Roylance slide rule by Keuffel and Esser in their 1913 catalogue (more correctly the addendum to the

1913 catalogue).

A fellow collector Mr David Rance has in his collection an early A.W. Faber Elektro (398-like) with

design numbers DGRM 271169 & 247514, this rule confirmed by Mr Guus Craenen in his forthcoming

book is actually a A.W. Faber 368 rule ( note, this is not referenced in either ref [5] or [6]) . Both

Registered Designs are credited to A.W. Faber for the years 1906 and 1905 respectively in ref [5]. The

271169 DRGM refers to a cursor extension and not to any specific electrical scale, the 247514 however

refers to an index edge at the end of the slide. This index edge is the first such mention of what was to

become the defining feature of an Elektro rule, note that this DRGM dates from 1905.

There is also evidence of a Dennert & Pape rule, the number 15, which I believe was produced in 1905

(again confirmed by Mr Guus Craenen) which incorporated elektro scales in the well. This rule also

incorporated log-log scales on the front of the rule according to the principles of the DRGM 148526 of

1901 awarded to Mr W. Schweth. This rule which had electrical scales in the well and log-log scales on

the body of the rule would become the spirit of the Elektro rule for the next 70 years, alas I do not have a

scan of the rule but by the courtesy of Mr Rance and Mr Craenen, I can show the Faber 368 and Nestler

32.

The AW Faber 368

The Nestler 32

Types of Rules It is Faber-Castell with their models 368, 378 and 398 (1/98 in later years) that seem to have established

the defining feature of a number of Elektro rules in placing the motor/dynamo efficiency and voltage drop

scales in the well of the slide rule and having some form of extension to the slide to read them. This layout

was used by so many of the mainstream manufacturers that it came to define the layout of the Elektro rule.

The reasons for this layout lie in the choice of the standard Rietz rule for the basis of the Elektro rule.

With the addition of usually two LL scales most of the rule “real estate” was utilized and the only

available space was the well underneath the slide Ref [8]. (Note that the Darmstadt rule used a different

approach and placed extra scales on the rule edges). To read the well scales, manufacturers produced a

variety of methods. Some examples are shown in the following diagrams:

Faber Castell 1/98 PIC PC18 PIC 131

Politehnica Simplon Aristo

The well layout is usually of the form as shown in the next diagram.

Most other rules had the efficiency and voltage scales set either above or below the principal scales.

A number of examples are shown:

Blundell Harling 305

Faber Castell

However, some manufacturers didn’t include specific scales for efficiency and voltage drop on their rules.

Instead they used gauge marks for these calculations, examples are Nestler 37 and the Unique Electrical.

The following diagram shows the Unique and you can see the gauge marks W and N for the motor and

generator efficiency calculations.

Unique Electrical

Another unique feature (no pun intended) are the extended temperature scales up to 300 degrees

centigrade and 600 degrees Fahrenheit. These are most useful for the electrical engineers engaged in

transmission line design where conductor temperatures are designed to at least 120oC.

Usual Scale Layouts of Elektro Rules Apart from the treatment of the scales required for the calculation of motor/dynamo efficiency and voltage

drop the scale layouts of Elektro rules generally followed a standard system.

The scales usually included:

• Standard A (x2), B (x

2), C (x), and D (x) scales

• CI (1/x) on the slide

• K (x3) scale which could be placed on the stator or on the lower edge of the rule and read with a

cursor extension

• L (log10) scale which could be placed on the stator, the reverse of the slide or on the lower edge of

the rule and read with a cursor extension

• S (sin) and T (tan) on the reverse of the slide.

• And two exponential scales, usually indexed to the C scale and extending over a range of 1.1 to

105

Some examples of these layouts are presented in the following diagrams with comments on the usefulness

of the layouts.

White & Gillespie 432 back White & Gillespie 432 Front

The only Australian rule that could be termed an Elektro rule, a standard set of scales although labelled

somewhat differently than the accepted notation eg Cu (Cube) for the K scale and Reciprocal for the CI

scale. It is fairly unique in that it is a duplex rule and most of the normal Elektro layouts used the simplex

design.

The classic Faber Castell 1/98

This is a standard layout with the special scales in

the well and extensions on the slider to read the

results. The two exponential scales are indicated

on the top and bottom edges of the stator. The K

scale is placed on the bottom edge of the rule and

is read by a cursor extension and the S, L, T scales

are on the reverse of the slide. Interestingly the S

scale is indexed to the A scale and the T scale is

indexed to the C scale, a system also used on the

Hemmi 80K. This allowed the S scale to range

from 34 minutes to 90 degrees and dispense with

the ST scale.

The Aristo 915E

This is a later Elektro design by Aristo where they

had discarded the slide extension and scales in the

well in favour of including them on the body of

the rule.

The Skala (Polish) Elektro

All scales are included on the front face of the

rule, which made for a wide body rule of some

62cms. Notice on the A scale the gauge marks for

what I assume to be two different alloys of copper

conductor. And the P (Pythagoras) scale! A

noticeable omission on many Elektro rules.

The Romanian Politehnica

Looking at this layout a number of differences to

the norm immediately come to notice. Firstly,

three exponential scales that extended the range

downwards to e0.01x also a folded B scale and

it can be seen in the following full scan of this

rule. The scale is only a half scale and the other

half of the scales’ position is taken up by another

interesting half scale. A closer inspection shows

this to be a PIC-like differential trig scale but

scaled in Grads not degrees as on the

PIC/Thornton Rules, the only other rule where I

have seen these scales used. But more

importantly there is a P (Pythagoras) scale

included.

A full scan of the Politehnica, which shows the two half scales that to my knowledge are unique. A half

folded B scale and an IC scale that is similar to the PIC differential trig scales but scaled in Grads.

The Blundell Harling 305

An uncluttered arrangement of scales with the S, L,

T scales on the reverse of the slide. One interesting

aspect of this rule is illustrated in the following

diagram, an extension of the efficiency scale for

three-phase motors and dynamos or more

accurately for alternating current systems an

“alternator” scale.

The Ricoh 107

This rule has departed from the usual scale

placement. Ricoh moved the trig scales to the

bottom of the stator and placed the exponential and

log scale on the reverse slide of the slide. A similar

arrangement to the well-known Darmstadt system.

The PIC 144

This rule has an unusual scale placement. The scale

layout uses a system promoted by a Dr AE Clayton

and arranged the trig scales so that sin, cos and tan

could be read directly for any angle, to 3 minutes. It

also added a Z scale to facilitate the calculation of

the sqrt of the sum of squares. The slide included on

the reverse side two log log scales from 1.1 to

100000 on the D scale and a Dec log log scale from

.98 to .15 on the A scale. The reverse also included

a C scale to ease the use of the slide when reversed.

A Staedtler 54106

This rule appears to be an exact copy of the Nestler

37 or 370. Same scale layout and markings and the

same cursor extensions to read the single LL scale

and L scale on the bottom edge. Note the single LL

scale. This scale worked with the A/B scales and

extended over the normal range of 1.0 something to

105 which is a similar range to the normal two LL

scale rules, albeit with less resolution. The V scale

used for calculating the voltage drop along a copper

wire, was matched to the C and D scales, and the U

scale, folded at pi/6, was also provided, this scale

was used angular speeds of machines.

The ALRO 600 E

One of the few examples of an “Elektro” circular

slide rule that I know of, except for such special

rules as the Kesel Circular Rule described in Issue 6

of the UKSRC Gazette [Ref 9]

Scan from Hermans Archive [Ref 3].

The UTO 611 ( a 12.5cm Elektro rule)

Most manufacturers made 5 inch (12.5cm) versions of their Elektro rules and they where exceedingly

popular with engineers as they could easily carry these instruments around in shirt pockets (most probably

close to the pen protector!!). The rule shown is of interest as it dispensed with the useful LL scales and

moved the Volt Drop and Efficiency from the well to the front of the rule. But it did include double Cos phi

scales, other rules that use this scale are the Nestler 0137 and the Pickett N16.

Gauge Marks There are many gauge marks on Elektro rules. Most can be explained but some require lengthy research in

the absence of the original manuals. The most common are listed below. To compile this list I have relied

upon manufacturers’ manuals and the most timely production of the “Pocketbook of the Gauge Marks” by

Panagiotis Venetsianos, an excellent reference book Ref [7] that was published just before I started

writing this paper.

Gauge

Mark

“Panagiotis”

Symbol

Explanation

1124 Cu Reciprocal of 8.9 specific weight of Cu

1257 4π 1.2566 = 4π/10 used for Electro magnetic induction calculations

134 N Reciprocal of 746 watts used as dynamo efficiency gauge mark of

the Unique Electrical Rule

136 DYN 1359 = reciprocal of 736 (watts in a metric HP) used as the dynamo

efficiency gauge mark of the Nestler 37 type rules

1414 √2 1.414 = Sqrt (2)

1481 Cu Resistance of copper whose resistivity is 0.01722 Ω.mm2/m at 20

degrees C

1493 Cu Resistance of Cu whose resistivity is 0.175 Ω.mm2/m at 20 degrees

C

1495 c Resistance of Cu whose resistivity is 0.1755 Ω.mm2/m at 20

degrees C

1732 √3 1.732 = Sqrt (3)

175 ρCu Resistivity of Cu 0.0175 Ω.mm2/m

175 kW Coupled mark for kW/HP conversions

1785 Cu Resistivity of Cu 0.01785 Ω.mm2/m

1854 A Resistivity of Al 0.027 Ω.mm2/m at 15 degrees C

1922 Al Resistivity of Al 0.029 Ω.mm2/m at 20 degrees C

218 AL Specific weight of Al

22 220 220 volt systems

238 PS Coupled mark for metric HP conversions

2408 - ? on a BRL E.13 rule

27 γAl Specific weight of Aluminium

2859 - Specific resistivity of Aluminium

287 - For finding the voltage drop in copper wires based on resistivity of

Cu 0.01742 Ω.mm2/m

29 ρAl Resistivity of Al 0.029 Ω.mm2/m

3049 V Resistivity of Cu of 23950 Ω.mil2/yd

3183 M Reciprocal of π (usually on the A scale)

332 W Specific weight of Cu

Gauge

Mark

“Panagiotis”

Symbol

Explanation

35 AL Conductivity of Al 35 m/Ω.mm2

3784 Cu Specific weight of Cu

38 C b Specific weight of Cu

38 380 380 volt systems

4429 √ Sqrt (2g)

572 Cu Conductivity of Cu 57.2 m/Ω.mm2

58 CU Conductivity of Cu 58 m/Ω.mm2

6283 2π = 2π

632 PS Coupled mark for metric HP conversions

6867 A Specific weight of Al

688 A Specific weight of Al

7071 Si Reciprocal of Sqrt (2)

735 MTR Watts in a metric HP

736 MOT or PS Watts in a metric HP also used as the motor efficiency gauge mark

on Nestler 37 type rules

746 HP Watts in a British HP

746 W Used as the motor efficiency gauge mark on the Unique Electrical

Rule.

75 ks 75 kgm/s – 1 cheval-vapeur (i.e. a metric HP)

89 γCu Specific weight of CU

9866 HP 0.98659 cheval-vapeur = 1 HP

These are the more common gauge marks but depending on the grade and alloy of copper or aluminium

there can be any number of gauge marks. For example the Roylance slide rule from K&E had numerous

standard wire gauge marks and the Skala rule has marks designated Cuk and Cun at 1818 and 1894

respectively. Which I can only assume are related to the resistivity of copper.

Some problems and how they where solved on an Elektro Rule This section should be prefaced by the fact that the scales on Elektro side rules where in general arranged

for direct current (DC). This may have been the case in the early 1900’s but alternating current (AC)

became the norm very quickly. And although the Elektro scales can, in general, be used for AC resistive

circuits, alternating current brings to the engineer a new set of complications such as impedance instead of

resistance, skin effects, frequency, capacitance, inductance and resonance.

Dynamo or Motor Efficiency Calculations Ref [1]

These were relatively simple problems which occurred with single phase motors that really did not require

a separate scale for the solution. In fact many Elektro rules dispensed with this scale completely and relied

on gauge marks for the calculation. In essence the scale did the conversion of horsepower (HP or PS) to

kW (kilowatts) in the division of input and output of either a motor or generator. The scale was actually a

composite scale consisting of part of one decade of an A scale followed by part of one decade of an AI

scale. The end index of both represented 100%, and was located over 7.46 (or 7.36 for a PS system) on the

A scale, as that represented a constant for converting kilowatts to horsepower. Since the efficiency of both

a dynamo or a motor must be less than unity, and that of a dynamo is expressed in terms of kilowatts per

horsepower, while that of a motor is expressed in terms of horsepower per kilowatt, this arrangement

served to convert both to efficiency in percentage terms.

When this scale was located on the body of the rule, the 100 percent mark was directly over either the 7.46

or 7.36 mark, when the scales where located in the well the 100 percent mark was placed such that when

the slide extension was over the 100 percent mark the index on the B scale was directly opposite the

relevant conversion quantity.

An interesting variation of these scales were the three-phase scales found on the Aristo 814, 914 and

Blundell Harling 305 rules. As the equivalent input or output calculations for a 3 phase system contains a

factor of 1.73 (√ 3) these scales are displaced by the conversion factor divided by 1.73. Therefore in the

case of the Blundell rule (English system) the 100% efficiency mark for three-phase systems is placed

above 43.1 on the A scale and in the case of the Aristo 914 (PS system) it is placed above 42.5 on the A

scale.

The use of the usual Dynamo-Motor scale can be illustrated by the following examples, one using the

specific scales and the other using gauge marks.

The basic equation to be solved;

Efficiency = Electrical energy output / Mechanical energy input.

Example:

Calculate the efficiency of a dynamo which gives an output of 13.5 kW for 21.0 HP.

Faber Castell 1/98 Elektro

Set 2.10 on the B scale against 13.5 on the A scale.

Read the efficiency, 86.2% on the Dynamo efficiency scale in the well of the rule.

As a check, 21.0 multiplied by 0.746 is 15.67 and 13.6 / 15.67 is 86.2. As you can see it is not a

complicated calculation, and personally I found it much easier to perform than to remember the actual

scale settings. And as one usually needs to convert HP into watts for other calculations it was to some

advantage to perform the calculation this way.

To perform the same calculation on the Unique Electrical it is necessary to use gauge points.

Set the output 13.5 kW on the D scale against the input 21HP on the C scale.

Read the efficiency, 86.6% on the DF scale, opposite the gauge mark N on the CF scale.

For most rules (i.e. ones with the special scales) the calculations of motor efficiency are simple mirror of

the calculations for dynamo efficiency. However, for the Unique and others with gauge marks, the

procedure is different.

Example:

Calculate the efficiency of a motor which develops 150 HP for 128 kW.

Set the output 150 horsepower on the D scale against the input 128 kW on the C scale. Read the answer,

87.5%, on the DF scale opposite the W gauge mark.

So although different, a consistent process is used. Place the output on the D scale opposite the input on

the C scale. For motor efficiencies read the DF scale opposite the W gauge mark. For dynamo efficiencies,

read the DF scale opposite the N gauge mark. But I wish manufacturers would have labelled the gauge

marks MOT and DYN! But why where the gauge marks put in these particular locations? Firstly, notice

the N mark, it is placed at 134, the reciprocal of 746 or the number of watts in a horsepower. The

calculation divides the input 21 horsepower by the output 13.5 kW on the normal C and D scales. Thereby

if the result is multiplied by the reciprocal of 746, the answer is obtained. As efficiencies are normally in

the range of 80 to 100%, the folded scale arrangement ensures that the answer can be read on the rule.

Compare this calculation with a rule that has A, [B, C], D scale arrangement.

Also worthy of note is the use by Unique of the C and D scales for these calculations. Almost invariably

other manufacturers used the A and B scales (and even Nestler used the A and B scales with gauge

marks). The reasons why they used the A and B scales escapes me. I have always found that one-order C

and D scales prevented confusion with the number setting. And the use of one-order scales i.e. the CF and

DF scale for reading the efficiencies allowed the result to be read with greater precision.

Voltage Drop Calculations Ref [1]

Voltage drop is given by the formula:

V = (I * L)/ (C * A)

Where:

V is voltage drop (volts)

I is the current (amps)

L is the length (yards)

C is the conductivity of copper

A is the section of the conductor.

Typical units for A are square inches, square millimetres and circular mils. Circular mils are calculated

from the diameter of the wire in thousandths of an inch squared.

The following calculations all assume copper wire and direct current.

Example:

Calculate the volt drop in a copper conductor 131 (119.7 m) yards long, 0.14 in (3.56 mm) diameter,

carrying a current of 20.4 amps.

The area of a wire 0.14 diameter is 0.0154 in2, equivalent to 9.94 mm

2 and 19600 circular mills (=140 *

140).

Faber Castell 1/98 Elektro The Faber Castell 1/98 is set up for units of 10 amps, 10 yards and 10000 circular mils.

Align 1 on the B (length and area) and scale against 2.04 (2.04*10amps = 20.4 amps) on the A

(current) scale.

Cursor to 13.1 (13.1 * 10 yards = 131 yards) on the B (length and area) scale.

Align 1.96 (1.96 * 10 000 circ. mils = 19600 circ. mils) on B (length and area) scale.

Read the answer 4.14 volts in the well of the stock.

Unique Electrical Area is 1402 = 19600 circular mils.

Set 1 on C against 2.04 on D.

Move cursor to 1.31 on C.

Move 1.96 to the cursor.

Read volt drop, 4.16, above V on the CF scale.

Note the similar result, although not identical. This could only be the case if all manufacturers agreed on

using the same copper cable alloy or agreed to use pure copper as the material for specific resistivity or

conductivity. A perusal of various manufacturers rule, manuals and also the recent publication

“Pocketbook of the Gauge Marks” by Panagiotis Venetsianos Ref [7] provide any number of resistivities

in use. A number of these are indicated in a later clause on Gauge Marks.

It is also interesting to note that usually Metric rules give an answer that is double the voltage drop

calculated above, e.g.

Faber Castell 378

The Faber Castell 378 is set up for units of 10 amps, 10 metres and 10 mm2.

Align 1 on the B (length and area) and scale against 2.04 (2.04*10amps = 20.4 amps) on the A

(current) scale.

Cursor to 11.97 (1.197 * 10 metres = 119.7 metres) on the B (length and area) scale.

Align 0.994 (0.994 * 10 mm2 = 9.94 mm

2) on B (length and area) scale. Here, as the 378 has scale

extensions the answer 8.5 volts is read in the well of the stock. This doesn’t equal 4.1 something.

WHY?

As can be seen the answer is twice the value given by the other rules and should be multiplied by 0.5. A

similar result is obtained using a Graphoplex Elektro rule. Why is this the case? I believe it results from

the way the problem is stated and formulated. In the “English” rules i.e. ones with units of yards, mils or

sq ins, the problem is thought of in isolation to any other system. The calculation is based upon current

through a single resistance. Whereas in the metric system, the designers assumed that the calculation was

to solve the problem of voltage drop from source to load and to therefore determine the voltage available

at the load. This can be illustrated by the following diagram:

As we can see in the practical world transporting power to a load requires a return path through which the

current has to travel. Therefore using the resistance of the length of wire to a load would not produce the

correct total resistance and a factor of two would be required. Therefore the designers of the metric rules

built this factor into their rules. It also explains why on some rules a gauge mark at 28.7 exists. This is the

reciprocal of twice the resistivity of copper (0.01742 Ω.mm2/m). Using this figure the correct value of

conductivity for the metric or two-wire solution can be used in the formulae for Voltage Drop.

A discussion with another collector (Richard Hughes) has introduced the quandary. Should the "two-wire"

solution be multiplied by 0.5 to agree with the "one-wire" solution or should "one-wire" solutions be

multiplied by 2 for the real world as discussed? My preference is still for the one-wire calculation, as this

is ubiquitous. The two-wire solution presupposes the calculation to be for a motor or load situation

whereas the one-wire solution is a basic calculation of current through a resistance. If the calculator is

aware of the problem (as they should be!!) then it is quite normal to add twice the length if this is the

nature of the problem. Richard has a number of Elektro’s in his collection

Nestler 0370 (March 65) L in metres and q in mm squared;

Aristo 915 (Jan 69) meters and mm squared;

Faber-Castell

• 1/98/398 (Feb 38) yard and Cmil;

• 1/98/398 yard and Cmil;

• 1/98 (March 66) yard and Cmil;

• 1/98 (Jan 71) metre and mm squared;

• 67/98 b (Jan 74) metre and mm squared.

All of these are the "one-wire" types. Another Elektro in his collection is the Sun-Hemmi 80K (Dec 65?)

which is a “two-wire”. Thus Richard has several "metric" versions that are of the "one-wire" type.

Therefore my previous hypothesis is not entirely correct. So is this another dilemma for the collector i.e.

how many Elektro rules are “English” rule “one-wire” types and how many are “Metric” rules “two-wire”

types?

Modern Day Practical Problems and the scales that would have helped. As seen in the earlier sections of this article, the problems that the Elektro rules tried to address are mainly

concerned with Motor and Dynamo efficiencies and voltage drop along copper conductors. However, as

most areas of life have evolved in the face of a changing technological age, so has electrical engineering.

No longer do we rely on direct current as power distribution medium (if ever) or copper conductors to

transmit electricity. The electrical engineer is probably more interested in problems of the following

nature:

Alternating Current (AC) Power Calculations

Calculation of power in direct current systems involved the direct application of Ohm’s Law where

Power = Voltage * Current

However, in alternating current systems the voltage and current can be out of phase. This is illustrated in

the following diagram:

Resistive Circuit Reactive Circuit

Power is then described as:

Power = Voltage * Current * Cosine θθθθ

Where θθθθ is the phase angle between the two waveforms. This calculation would be easily facilitated by a

cos scale on the slide.

Three-Phase Power

The above equation applies to single phase systems, however the majority of electricity transmission and

distribution systems uses the three-phase system. The power delivered by such three phase systems can be

calculated by the following formulae:

P = 1.73 * Line Voltage * Line Current * Cos θθθθ

The value 1.73 is the square root of 3. Again calculation of this formula would have been made easier with

the addition of a gauge mark at 1.73 on the C or D scale. This is a surprising omission on most Elektro

rules.

Impedance Calculations

The impedance of an ac system is the equivalent of resistance in a dc system. However where resistance is

scalar, impedance is a vector quantity and is usually quoted as a complex number in terms of:

R+ jX ohms (the Cartesian form) where R is the real (resistive) component and X is the imaginary

(reactive) component

Or

Z ∠φ ohms (the Polar form) where Z is the magnitude (impedance) and φ is the angle (phase)

The key to determining impedance is the calculation of reactance and depending on whether the reactance

is capacitive or inductive the reactance is given by the following equations:

C∗ω1

Ohms if Capacitive or L∗ω Ohms if Inductive

Where ω is equal to 2π times the frequency of the alternating current. This calculation is carried out

numerous times a day by a practicing electrical engineer. It would be extremely convenient if gauge marks

where added to the Elektro rules. It is surprisingly that this was the exception instead of the rule. However,

50 cycles/sec (hertz) countries had an advantage in this area as 2πf was equal to 100π. So the π mark

doubled as the gauge mark. However, in 60 Hz countries, 2πf was equal to 377. This is nowhere to be

seen on any rule I have in my collection and it even doesn’t rate as a known gauge mark in Mr

Venetsianos’ book. The reciprocal of 2πf is also equally useful for calculation of the capacitive reactance

and thus gauge marks at 3183 and 2653 would be advantageous, but again 3183 is not common and 2653

is never seen. Another technique or scale addition that would have assisted in these calculations would

have been to include a CF and DF scale folded at ππππ or even more useful folded at 2ππππ..

Polar to Rectangular conversions

The concept of impedance was identified in the previous section and could be written in the cartesian form

or the polar form. Each form offered an advantage, multiplication and division is easier if vectors are in

the polar form, addition and subtraction is easier if the vectors are in the rectangular or Cartesian form.

Thus polar to rectangular conversions and vice a versa were common everyday practice for engineers in

this discipline.

The mechanics of the conversion from polar to Cartesian and vice a versa can be demonstrated via simple

trigonometry relationships

For instance:

In the impedance triangle above, the relationship known as the sine rule specifies;

( ) ( ) ( )zSin

Z

rSin

R

xSin

X== = Z (as sin 90 =1)

And as the polar form of an impedance vector is usually quoted as Z∠x for example use 5∠30° ohms

5)3090sin()30sin(

=−

=RX

X and R are easily solved, and the calculation is fairly efficient on a rule with the trig scales on the back of

the slide. For X in the above formulae, place 30° on S scale to the index mark on back and read the

answer, 2.5 on C scale, against 5 on D scale. For R, place 60 on the S scale to the index mark on the back

and read the answer 4.33 on the C scale against 5 on the D scale.

If the trig scales are on the front of the slide the method is as efficient. However, an additional advantage

of trig scales on the front of the slide is in chain calculations involving trig values and I would have

preferred to see a rule with a larger slide so that at least a sine scale could have been included

Power Factor

Power Factor (PF) is the ratio of active power to apparent power and is equal to the cosine of x in the

impedance triangle shown previously. If the PF of a power system load is given as 0.8 then the engineer

knows that the resistive component is 0.8 times the impedance and conversely using the Pythagorean

relationship the reactive component is 0.6. This calculation is a straightforward conversion if the slide rule

contains a P scale.

Consider the following example. An electrical load of 100 kVA has an effective power of 85kW.

Therefore cos x is 85/100 or 0.85. Setting 0.85 on the D scale provides the answer for reactive power of

52.9 kVA on the P scale.

The addition of a P (Pythagoras) scale would have been more than convenient, but rarely provided on

Elektro rules. The P scale would have also assisted in polar to rectangular conversions.

Exponential Decay

In any switching of electric circuits containing inductance and/or capacitance, the rise or decay of current

and voltage depends on a time constant that is established by the values of reactive and active components

of the system i.e. the resistance and inductance/capacitance. For a circuit containing resistance and

inductance the relationship for current is:

∗=

−− L

Rt

e1Impedance

VoltageCurrent

Similar equations can be written for voltage and also for capacitive circuits. Notice the exponential

function is in terms of a negative number. The consequence is that the equation tends towards steady state

solutions equal to the value of voltage divided by impedance. On rules that have only positive LL scales

like Elektro rules this is an inconvenient equation. Of course we could always find the solution to ex and

then take the reciprocal, but it would be simpler to have inverted LL scales.

Currents in Long Transmission Lines

The relationship between voltages and also currents in long transmission lines can be realized by the

following equation:

ZYErEs cosh= +Y

ZIr ZYsinh*

Where the subscripts s and r stand for the sending end and receiving end and Z is the series impedance of

the line and Y is the shunt admittance ( the reciprocal of the impedance to ground) of the line. For most

electrical engineers in the electricity supply industry this is a well known and not uncommon equation.

Hyperbolic functions would be a nice addition to the slide rules.

Catenary Calculations

The suspension of cables from electricity pylons also is expressed in terms of hyperbolic functions ref [4].

For example:

−= 12

coshC

SCy And

C

SCL

2sinh2=

S is the span, s equals the sag, L is the length to the point of sag and C is a constant. Again, hyperbolic

functions would have been an advantage.

Missing P Scales, WHY? There is a continuing question with “Elektro” rules. That, in a discipline that has, as an important and

frequent calculation, many polar to rectangular conversions and power factor calculations, why there isn’t

a “P” scale included on many Elektro rules.

In all of the “classical” rules the P scale does not feature, why?

Is this a legacy from the days of direct current where complex mathematics did not feature or was it a

preference of distribution engineers where impedance was not an important concern? The origins of

Elektro rules begin in the early 1900’s when Direct Current (DC) was much more common as a

distribution medium than Alternating Current (AC). But AC was soon the dominate system as it made

transportation of power far easier for large distances and allowed easy conversion between voltage levels.

So I doubt that the manufacturers of the rules would not be aware of such changes in technology.

Was it because of the adoption of the standard Rietz pattern, and the available space was restricted?

Perhaps in the practical application of electric problems of voltage drop and motor efficiency, the

designers of the rules where being pragmatic and contended that there is little difference at the low

voltage, low frequency level between the two systems. But in the daily working of an electrical engineer,

even at distribution voltage levels (110 volts to 11,000 volts) calculations of impedance required polar to

rectangular conversions and power factor calculations. The particular advantage offered by a rule with a P

scale was and is obvious to many people, but apparently not to the manufacturers of Elektro Rules.

Improved versions of “Elektro” Rules Although mentioned in the Hemmi 1931 catalogue the model 153 could be called the first improved

version of the Elektro side rule. This rule used a “theta” scale and also an indexed radian scale (Re) in

cooperation with the “un-logarithmic” scales called the square P and Q scales. But the strangest scale of

all on the 153 was the Gudermanian scale “Ge”.

The Gudermanian function, named after Christoph Gudermann (1798 - 1852), relates to the circular and

hyperbolic trigonometric functions without resorting to complex numbers. The identities can be defined as

follows;

The actual usage and development of this scale on Hemmi rules was invented by Hisashi Okura and a US

patent was issued in 1937.

To obtain hyperbolic values of an argument x the Ge, T, P, Q and Q’ scales where employed. Although

the uses of the special scales on the 153 are not particularly intuitive they were, by and large useful in

vector calculations. After some practice, the Ge scale provided very easy way to calculation of at least

Sinh and Tanh values without the need for hyperbolic scales.

The Romanian rule depicted earlier seemed to combine most of the so called improvements required by a

‘normal” Elektro rule.

Some of the improvements or additions to the normal Elektro rules are:

the addition of a P scale,

the addition of an extra LL scale down to e 0.01x,

the metric system (10m and 10mm2 for conductors),

an ST scale for small angles,

scale extensions to 0.7854 (i.e. to at least π/4 the constant factor for the area of a circle).

This rule was probably produced in the late 60’sand the 1970’s and so benefited from hindsight.

An “Ideal” ELEKTRO Rule It would be hard to define such thing but given the previous dialogue I could offer a number of scales and

gauge marks an ideal rule might have:

• Standard A (x2), B (x

2), C (x), and D (x) scales.

• CI (1/x) on the slide.

• K (x3) scale which could be placed on the stator or on the lower edge of the rule and read with a

cursor extension. Although this is a usual scale included on Reitz and Darmstadt rules I found this

scale little used in electrical engineering calculations and would have easily dispensed with this

scale for the inclusion of some of the scales listed below.

• L (log10) scale which could be placed on the stator, the reverse of the slide or on the lower edge of

the rule and read with a cursor extension.

• S (sin) and T (tan) on the reverse of the slide.

Note the preceding are standard scales appearing on nearly every Elektro rule and follow the normal Rietz

pattern.

• I would dispense with the actual “defining” scales for an Elektro rule (i.e. the Volt drop and

Motor/Dynamo efficiency scales) in favour of gauge marks similar to the Nestler and Unique rules.

The classic scales take up valuable rule real estate and as Snodgrass in his book “The Slide Rule”

[Ref 2] points out, efficiencies are nearly always in the order or 80 to 90% thus the answer is

always in a crowed part of the rule if using small 5 inch special scales. Voltage drop calculations

are always dependent on the value of resistivity assigned to the conductor metal. They would be

better dealt with via gauge marks for the particular conductor resistivity or by a special purpose

rule such as the Voltage Drop Slide Rule by C.C. Moler which was described in JOS Vol 11, No.1.

Other examples speciality rules are:

BICC PF and Voltage Drop Rules BICC circular Voltage Drop Rule Note: BICC is an acronym for British Insulated Callender’s Cables

The additional scales proposed are:

• Positive LL scales in the range from .01 to 10 at least and if real estate allows inverted LL scales.

• Extra Sin and Cos scales on the slide to assist with chain and power calculations.

• CF and DF scales folded at 2π or at least π.

• Hyperbolic Functions.

• Pythagoras scale (ideally two similar to the Aristo MultiTrig as power factors are nearly always

between 0.85 and unity).

• Other possible scales but not essential would be a CIF scale and a Ln scale.

• The inclusion of Gauge Marks, other than those already suggested for voltage drop and efficiency

calculations, at:

sqrt of 2 and 3,

2πf for both 50 and 60 Hertz systems,

746 and 736,

resistivity of Cu and Al.

All of these requirements would have meant a duplex rule and in the latter period of slide rule

manufacture duplex “Elektro” rules started to appear. One such rule was the Hemmi 255D:

As can be seen from the scans, it has:

the “standard” scales,

hyperbolic functions,

CF and DF scales folded at π,

a SI scale, an interesting idea in as such it is a Cos scale to the 84 degree,

a radian scale that can be used for degree to radian conversion,

the scale layout with the trig scales that allows for easy polar to rectangular

conversions.

There is however no gauge marks on this rule. The original purpose of Elektro rules has been given scant

regard and the defining scales have been completely omitted from this rule.

Another late era slide rule that incorporated everything that the Hemmi 255D did plus had space available

for the trad ional scales of Voltage Drop and Efficiency was the Flying Fish 6006. It even included dB and

Neper scales!

The scans of the Flying Fish 6006 are used with the kind permission of GuiSheng Xu and more details of

this rule can be found at his “Slide Rule Zone” website http://www.sliderule.com.cn

Or perhaps an ideal slide rule would look like this:

The above rule faces were built using the GriffenFly Universal slide rule package available from www.griffenfly.com.

As can be seen this rule dispenses with the normal Elektro rule scales for efficiency and voltage drop and

moves towards a scale arrangement to allow easy manipulation of vectors and added:

folded C and D scales around π,

matched sets of S and T scales,

extended range P scales,

four Log-Log scales,

hyperbolic functions,

a Ln scale.

Conclusion I hope the paper has provided some insight into the requirements of a slide rule by the electrical

engineering industry and engineers within the industry. Although the speciality scales of Elektro rules

provided answers to some common problems within the industry, these problems were in themselves

trivial and could be handled by simple calculation with the standard Reitz or Darmstadt rules. Then why

where these rules ubiquitous and produced right to the end of the slide rule era? I have no answer to this

question, except to add that maybe the simple Reitz layout with the addition of a couple of LL scales

produced an inexpensive and efficient rule that many people were comfortable with using this

arrangement.

Acknowledgements

I must acknowledge the valuable assistance of Ron Manley and his permission to use, without restriction,

the motor efficiency and voltage drop calculation descriptions from his web site. His permission and

assistance saved many hours of work and also provided accurate and succinct descriptions of these

calculations, far better than I could have achieved.

And I would also like to thank both David Rance and Richard Hughes for providing valuable suggestions

for the improvement of this paper and in particular David for his assistance in editing and his continued

support.

References

1. Ron Manley’s Web Page http://www.sliderules.info/

2. “The Slide Rule” by Burns Snodgrass

3. “Herman's Archive” by Herman van Herwijnen http://sliderules.lovett.com/herman/begin.html

4. “The Slide Rule – Principles and Applications” by Joseph Norman Arnold

5. “Slide Rules A Journey through Three Centuries” by Dieter von Jezierski

6. “Slide Rules – Their History, Models, and Makers” by Peter M Hopp.

7. “Pocketbook of the Gauge Marks” by Panagiotis Venetsianos

8. ‘The Slide Rule, Technical Cultural Heritage” by Ir. IJzebrand Schuitema

9. Slide Rule Gazette – A Publication of the UKSRC Issue 6 Autumn 2005

Appendix 1

Known Electrical or Electronic Rules

Data taken from ref [3], ref [6] and my collection

Rule (Manf, Model) Ele

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25 c

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12.5

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Special Scales G

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s

Scales Scales

Well

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e

Front Back

Ahrend 15 Electro (Dennert & Pape 15) • • • LL2 A = B C = D LL3 # Dyn-Mot V #

Ahrend 654 Electro • • • LL2 A = B C = D LL3 # Dyn-Mot V # = S T =

Alro 200R • • • S T S&T N2 N = N N2 R N3

Alro 600E • • • n2 C = D n2 LL Dyn-Mot V ? L

Antica Fabbrica Vittorio Martini Elettro Cosfi 401 • • • • V A = B CI C = D U = S ST T =

Antica Fabbrica Vittorio Martini Elettro Cosfi 416 • • • • V A = B CI C = D P K LL || L = S ST T =

Archimedes 18 C Electro • • A = B CI BI C = D L LL1 LL2 LL3 P = S T =

Aristo 814 Elektro • • • • LL2 A = B CI C = D LL3 #V D/M(=) ( opt G/M3~))# = S L T =

Aristo 815 Elektro • • • K A = B BI CI C = D D/M(=) V = S ST L T =

Aristo 914 Elektro • • • LL2 A = B CI C = D LL3 #V D/M(=) ( opt G/M3~))# = S L T =

Aristo 915 Elektro • • • K A = B BI CI C = D LL3 LL2 D/M(=) V = S ST L T =

Aristo 949 ? ? • ? ?

Aristo 1014 Elektro • • • LL2 A = B CI C = D LL3 #V D/M(=) ( opt G/M3~))# = S L T =

Aristo 1015 Elektro • • • K A = B BI CI C = D LL3 LL2 D/M(=) V = S ST L T =

Aristo 10175 • • • LC 2phi A = B CI C = D S T L Special Scales

Blundell 305 C Electro Academy • • • V Dyn-Mot G/M3~ A = B CI C = D K LL2 LL3 = S L T =

Blundell 404 Electro Omega • • • • LL2 A = B CI C = D LL3 # Dyn-Mot V # = S L T =

Blundell 604 Electro Omega • • • • LL2 A = B CI C = D LL3 # Dyn-Mot V G/M3~ # = S L T =

Blundell 805 Electrical Academy • • • V Dyn/Mot A = B CI C = D K LL2 LL3

Blundell E 3 Electrical • • • Volt A = B Cos C øF = D Dyn-Mot


ktr

o

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50 c

m o

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25 c

m o

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ch

12.5

cm

or

5 in

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Special Scales G

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Scales Scales

Well

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Blundell E 13 Electricians • • • K LL1 LL2 DF = CF 1) CRF CR C = D P LL3 A # Dyn-Mot V #

Blundell E 18 Electricians • • • V D A = B C = D øF øC cos # Dyn-Mot V #

Blundell E 25 Electricians • • • LL3 A = B R C = D LL3 K # Dyn-Mot V #

Blundell P 16 Electricians • • • Volt Dyn-Mot A = B cos C = D LL1 LL2 Res Cos

Colgate ? ? Mentioned in Ref 6

Concise 200 EE Data Center • • • D = C CI L A S T K M Data Tables for Resistance and Reactance

Concise 380 Radio Computer • • • Special Scales Special Scales

Concise EE - 112 • • • D = C CI L A S T1 T2 ST

Davis Electrical • • ?

Dennert & Pape 15 • • • LL2 A = B C = D LL3 # Dyn-Mot V #

Dennert & Pape 141 • • ? Mentioned in ref 5



Dennert & Pape 49/20 • • ? Mentioned in ref 5

Dimier Electric • • • kW A = B(cv) C = D(cv) # Dyn-Mot V # = mm2 mm =

Diwa 111 Electro • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V #

Diwa 311 Electro • • • K A = B CI C = D Volt tg. cin. = LL1 LL2 LL3 =

Diwa 511 Electro • • • Dyn-Mot K A = B CI C = D V tg. sin. = LL1 LL2 LL3 =

Diwa 611 Electro • • • cosj A = B CI C = D cosj # Dyn-Mot V # = LL1 LL2 LL3 =

Duval Regle Electro • • • L K A = B CI C = D LL1 LL2 LL3 #30-20# #0.5+10Volts# =cossin Tg C =

Faber Castell 319 • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V # = sin lg tg =

Faber Castell 368 • • • LL3 LL2 / A = B C = D / 27cm # Dyn-Mot V # = sin lg tg =

Faber Castell 378 • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 379 Elektro • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 388 • • LL2 A = B C = D LL3 # Dyn-Mot V #

Faber Castell 388 N • • LL2 A = B C = D LL3 # Dyn-Mot V #

Faber Castell 398 • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V # = sin lg tg =


ktr

o

Ele

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on

ic

50 c

m o

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ch

25 c

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ch

12.5

cm

or

5 in

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Special Scales G

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s

Scales Scales

Well

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Front Back

Faber Castell 1/78 Elektro • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 1/78/378 Elektro • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 1/98 Elektro • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V # = sin lg tg =

Faber Castell 1/98/398 Elektro • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V # = sin lg tg =

Faber Castell 111/98 Elektro • • • LL2 A = B CI C = D LL3 Dyn-Mot V ] K = sin lg tg =

Faber Castell 167/98 Elektro • • LL2 A = B CI C = D LL3 Dyn-Mot V ] K = sin lg tg =

Faber Castell 379 Elektro • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 4/98 Elektro • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V # = sin lg tg =

Faber Castell 61/78 • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 61/78/379 • • • LL2 A = B C = D LL3 # Dyn-Mot V # = sin lg tg =

Faber Castell 61/98/319 Elektro • • • LL2 A = B CI C = D LL3 ] K # Dyn-Mot V #

Faber Castell 67/98 Elektro • • • LL2 A = B CI C = D LL3 Dyn-Mot V = sin lg tg =

Faber Castell 67/98 Rb Elektro Addiator • • • LL2 A = B CI C = D LL3 Dyn-Mot V = sin lg tg =

Flying Fish 1018 • • • LL01 LL0 LL1 K A = Q QI L I = D DI LL02 LL2 f Rf P’ P =B T S C = J J’ T Gf

Flying Fish 6006 • • • dB Neper V Dyn-Mot A = B T S C = D K P L Sh1 Sh2 Th Ch DF = CF CIF CI C = D LL3 LL2 LL1

Fuji 208 Electro • • • K E A = B CI C = D LL3 LL2 L = S ST T =

Graphoplex 643 Electro Log Log • • • L cos B3 B2 = b2 a b = B LL3 LL2 LL1 = S&T S T b =

Graphoplex 650 Electro • • • L B3 cos? B2 = b2 a b = B cos? Dyn-Mot V = S&T S T b =

Graphoplex 697 Electro • • • L 1) Dyn-Mot V A = B Cap./Ind. CI C = D f l DI

ST T S DF = CF CIF K CI C = D LL3 LL2 LL1

Graphoplex 698 Electronicien • • • f XC f XL A = B L Cap CI C = D f' f Log x-decibels

ST T S DF = CF CIF K CI C = D LL3 LL2 LL1

IWA 0272 Electronic • • • Lamda, Cw f = C L Rc = LC Rl K S T A = B CI C = D Ln cm

IWA PIA Electronic • • • A = B Cap, Ind C = D f l2/l1 db p/p = S L T =

Jakar 66 • • • K Dyn-Mot V A = B CI C = D LL3 LL2 L = S S&T T =


ktr

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50 c

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25 c

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12.5

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or

5 in

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Special Scales G

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Kesel • • • • K C R Special, Cu price, Cu wght, V, Eff, PS, Belt, Rev, PS, Cu dia

Keuffel & Esser 4133 Roylance Electrical • • •

A = B (F C) CI C = D ] B & S Wire Gauge # Wire Amp # = S L T =

Keuffel & Esser 4139 Cooke Radio • • LC A = B T ST S = D DI L DF = CF CIF CI C = D 2phi

Keuffel & Esser National Radio Union • • • Xr,Xc = F Ind = Cap

Lawrence 8-L Voltage Drop • 8" • Cable Distance = Current VD = Wire Size

Loga 30sE • • C = D Cos

Loga 30sT • • • Sqrt1 Sqrt2 D = C CI K L Cos

Loga 300 Tt.-El • • ? ?

Lyra - Orlow 41E • • • ? ?

Marcantoni 12.5 RE • • • cos? A = B CI C = D cos? # Dyn-Mot V # = S L T =

Marcantoni 25 • • • ?

Nelson - Jones Circuit Designers Slide Rule • • • db A = B CI C = D LL3 LL2 XL = L&C F = XC

Nestler 11ZE • • • cos A = B CI C = D cos # Dyn-Mot V # = S L T =

Nestler 32 Elektro (Presser) • • C = D A = V

Nestler 36 Elektro • • • • • LL2 A = B CI C = D LL3 = Dyn-Mot V =

Nestler 37 Elektro • • • • • V A = B C = D U // LL3 K #30-56cm# = S S&T T =

Nestler 39 Elektro (Besser system) • • • Special Scales

Nestler 0137 Elektro • • • Dyn-Mot Volt A =B CI C= D,P1 P2 = S L T =

Nestler 0297 Electronic I • • • Special Scales Special Scales

Nestler 0370 Elektro • • • V A = B C = D U ] LL3 K #30-56cm# = S S&T T =

Nestler 0374 System Moisson • • • 2πf Ind = Cap D/l D-n = Lambda f ?

Nestler 375 Elektro • • • V A = B C = D U ] LL3 K #30-56cm# = S S&T T =

Ohico Electro 15 • • • LL2 A = B C = D LL3 # Dyn-Mot V # = S L T =

PIC Electro • • • S A = B Dyn-Mot Volt C = D T = LL L K =


ktr

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50 c

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25 c

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PIC 130 • • • LL2 LL3 A = B CI (Isd ITd Td Sd) C = D K # Dyn-Mot V #

PIC 131 / 132 / 134 • • • • • LL2 LL3 A = B CI ISb Tb C = D P # Dyn-Mot V #

PIC 144 AC Electrical (model F) • • • S C A = B CI ( Z c f )C = D T // S T = LL1 LL2 LL3 C =

PIC 141 AC Electrical (Model E) • • • S C A = B CI ( Z c f )C = D T // S T

PIC Electrical • • • • • LL1 A = B CI C = D LL2 D&ILL # V Dyn-Mot # = S T L =

Pickett N16ES • • • SH1 SH2 TH DF = CF L S ST T CI C = D LL3 LL2 LL1 Ln 21 special scales

Pickett N515T Electronic • • • (Lr)H (fx)2phi A = (Cr)B S T (Lx or Cx)CI xL or fr-C = D L Ln Special Scales

Pickett N531 CREI Electronic • • • L Ln A = B CI C = D 2Phi K LL2 LL1 = S ST T C = D LL3

Pickett N535 Electronic • • • L Ln A = B CI C = D 2Phi K Special Scales

Pickett N931 Electronic • • • L Ln A = B CI C = D 2Phi K LL2 LL1 = S ST T C = D LL3

Pickett N1020 NRI • • • K A = B ST T S C = D DI 2Phi DF = CF L CI C = D DI

Reed Service Electronic Engineers • • • • K A = B CI C = D L #D/L# = S S&T T =

Reiss Elektro • • • K A = B CI C = D L LL2 Dyn-Mot = sin sin/tg tg = V LL3

Relay 157 • • • Sh2, Sh1, A = B, K, Th, C = D, Tr1, Tr2, dB Sr, S theta, P', P = Q, CF, CI, C = D, DF, LL2, LL1

Relay 158 • • • Sh2 Sh1 Th A = BI S T CI C = D LL3 LL2 LL1 X1 X2 P2 P1 = Q Y L Lx I =

Relay 605 • • • Dyn-Mot L1 A = B CI C = D L2 Volts = S L T = Eq. Tbl

Ricoh 107 • • • Dyn-Mot V A = B K CI C = D S T = LL3 LL2 LL1 L =

Ricoh 156 • • • db DF =CF CIF CI C= D A Xc XL K =KI S T= F2 F1 DI

Rista 2 Electro • • • Motor K A = B CI C = D Volt T S = LL1 LL2 LL3 =

Rista 22 Electro • • • Dyn-Mot V A = B CI C = D COS COS L = S S&T T =

S.R.E ELEKTRON 25 • • • S T F A = B CI C = D P R I/I0 dB P/P0

Seehase Elektro Praktikus • • • Special Scales

Sydney Service Rule • • • LL2 A = B C = D LL3 = S L T =

Tianjin Gong Nong Bing 6504 • • • T1 T2 K A = B F CI C = D L S LL01 LL02 LL03 SG1 = SG2 SG2' C R1 =


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Simplon Electro Log-Log • • • LU A = B CI C = D LL # Dyn-Mot V # = A S T D = L D

Skala • • • Pradnica Silk Volt L P K A = B CI C = D LL3 LL2 S T s-t

Staedtler 54106 Electro • • • V A = B CI C = D U ] LL3 K = S S&T T =

Stanley "Electrical or Mechanical engineers Rule" • • • LU A = B C = D LL # Dyn-Mot V # = S L T =

J. Hemmi 4 • • • LL2 A = B C = D LL3 # Dyn-Mot V # = S L T =

Sun Hemmi 80 • • LL2 A = B C = D LL2 # Dyn-Mot V # = S L T =

Sun Hemmi 80/1 • • LL2 A = B CI C = D LL2 # Dyn-Mot V # = S L T =




Sun Hemmi 82 • • • LL2 A = B CI C = D LL2 # Dyn-Mot V # = S L T =




Sun Hemmi 86/3 • 15cm • Dyn-Mot V A = B CI C = D LL3 LL2 ] K = S L T =

Sun Hemmi 86 • 15cm • LL2 A = B CI C = D LL2 # Dyn-Mot V # = S L T =

Sun Hemmi 87/3 • 15cm • LL2 A = B CI C = D LL2 # Dyn-Mot V # = S L T =

Sun Hemmi 80K • • • Dyn-Mot V A = B CI C = D LL3 LL2 ] K = S L T =

Sun Hemmi 86K • • • Dyn-Mot V A = B CI C = D LL3 LL2 ] K = S L T =

Sun Hemmi 152 • • • K A = B CI C = D T Θ Rθ = P Q Q' C = LL3 LL2 LL1

Sun Hemmi 153 • • • L K A = B CI C = D T Ge L Re P = Q Q' C = LL3 LL2 LL1

Sun Hemmi 154 • • • DF P' = P Q CF CI S' = A D K S T = T' Th Sh C = D L X

Sun Hemmi 255 Electrical Engineering • • • Sh1 Sh2 Th A = B TI2 TI1 SI C = D Θ L K DF = CF CIF CI C = D LL3 LL2 LL1

Sun Hemmi 255D Electrical Engineering • • • Sh1 Sh2 Th A = B TI2 TI1 SI C = D DI Θ L K DF = CF CIF CI C = D LL3 LL2 LL2


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Sun Hemmi 256 Electronics • • • L db Neper DF = CF CIF CI C = D LL3 LL2 LL1 A L = C SI TI = D lambda F

Sun Hemmi 266 Electronics • • • LL3 LL1 LL2 LL2 A = B BI CI C = D dB L S T XL XC F r1 P = r2 Q L Cf Cz = L Z f0 l

Sun Hemmi 275D • • • L K DF = CF CIF CI C = D LL3 LL2 LL1

Sh1 Sh2 Th A = B TI2 TI1 SI C = D DI x Theta

Tavernier Gravert 2184 Electro • • • LL2 A = B CI C = D LL3 = Dyn-Mot V =

Tecnostyl 41/E Electro • • • cos A = B CI C = D cos = S lg T =

Thornton Electrical • • • LL2 A = B C = D LL3 # Dyn-Mot V # = S L T =

Thornton 3650 LL2 LL3 A = B CI C = D K # Dyn-Mot V # = S L T =

Timisoara Politehnica • • • P K A = B BF,IC CI C = D LL3 LL2 LL1 \ L R # Dyn-Mot V# = S ST T =

Unique Electrical • • • LL2 FAHR. CF = DF V CI C = D CENT. LL3

Unis Electricien No.5 • • • kW A = B C = D Dyn-Mot

UTO 551 - U Darmstadt Electro 1A • • • Motor K A = B CI C = D Volt T S = LL1 LL2 LL3 =

UTO 611 Richter Electro 22 • • • Dyn-Mot V A = B CI C = D cos cos L = S S&T T =

VEB Mantissa Electric • • • LL1 LL2 LL3 A = B L CI C = D P S T Special Scales

White & Gillespie 432 • • • LL L A = B Reciprocal C = D Cu LL Sine Kw = H.P. F Tangent = V Dyn-Mot

Westec Electronics Slide Rule • • • Lr K 2phi A = B S T CI C = D L Ln ST Special Scales

Woodworth (Electrical Wireman) ? ? (Lewis Institute, USA) mentioned in Ref 6

Woodworth (Volt, amps, ohms and watts) ? ? (Lewis Institute, USA) mentioned in Ref 6

Unknown Maker (Czech origin) No 11 • 10cm • L A = B CI C = D K = S ST T =

Elektro Rules Paper

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